1. Field of the Invention
The present invention relates to a circuit for detecting direction and amplitude of oscillations of a capacitive microelectromechanical system (MEMS) accelerometer, and more particularly, to a bidirectional readout circuit for detecting direction and amplitude of an oscillation by using an enable signal having a time change amount generated by capacitance-to-time converting capacitive changes of an MEMS accelerometer.
The work related to the present invention was supported by the IT R&D program of MIC/IITA [2006-S-054-02, Title: Development of CMOS based MEMS processed multi-functional sensor for ubiquitous environment]
2. Description of the Related Art
Microelectromechanical systems (MEMS) technology indicates a micro two-dimensional structure having a sensor or actuator function and a system including the same, in which micro mechanical devices, difficult to be distinguished with naked eyes, such as a sensor built-in a semiconductor chip and an actuator, are coupled with a circuit.
The MEMS technology provides core technology to Ubiquitous sensor network fields such as digital information detection, mass storage, micro displays, micro energy source, and wireless or wired communication. The MEMS technology is applied to components of various information devices such as magnetic and optical heads and utilized as accelerometers in automotive airbags.
Accordingly, researches on Readout Integrated Circuits (ROIC) for processing signals of sensors using the MEMS technology (hereinafter, referred to as MEMS sensors) are actively performed.
MEMS sensors may be largely divided into vector quantity sensors and scalar quantity sensors. The scalar sensors have no direction, such as sensors for temperature or humidity.
As representative vector quantity sensors, there are accelerometers. Capacitive MEMS accelerometers sense and convert displacement, velocity or acceleration, externally applied, into electric signals, which are manufactured using the MEMS technology and semiconductor integrated circuit processing technology. As representative capacitive MEMS accelerometers, there are accelerometers in automotive airbags.
As representative detection circuits used for ROIC of MEMS accelerometers, there are capacitance-to-time converters and time-to-digital converters (TDC), which are advantageous to high resolution. Such detection circuits are generally used for scalar quantity sensors since it is difficult to determine direction of a scalar quantity, such as time.